Efficient H2O2 Synthesis through a Two-Electron Oxygen Reduction Reaction by Electrocatalysts.

The two-electron oxygen reduction reaction (2e-ORR) for the sustainable synthesis of hydrogen peroxide (H2O2) has demonstrated considerable potential for local production of this environmentally friendly chemical oxidant on small, medium, and large scales. This method offers a promising alternative to the energy-intensive anthraquinone approach, placing a primary emphasis on the development of efficient electrocatalysts. Improving the efficiency of electrocatalysts and uncovering their catalytic mechanisms are essential steps in achieving high 2e-ORR activity, selectivity, and stability. This comprehensive review summarizes recent advancements in electrocatalysts for in-situ H2O2 production, providing a detailed overview of the field. In particular, the review delves into the design, fabrication, and investigation of catalytic active sites contributing to H2O2 selectivity. Additionally, it highlights a range of electrocatalysts including pure metals and alloys, transition metal compounds, single-atom catalysts, and carbon-based catalysts for the 2e-ORR pathway. Finally, the review addresses significant challenges and opportunities for efficient H2O2 electrosynthesis, as well as potential future research directions.

Open Active Sites in Ni-Based MOF with High Oxidation States for Electrooxidation of Benzyl Alcohol.

The kinetics of electrocatalytic reactions are closely related to the number and intrinsic activity of the active sites. Open active sites offer easy access to the substrate and allow for efficient desorption and diffusion of reaction products without significant hindrance. Metal-organic frameworks (MOFs) with open active sites show great potential in this context. To increase the density of active sites, trimesic acid was utilized as a ligand to anchor more Ni sites and in situ construct the nickel foam-loaded Ni-based trimesic MOF electrocatalyst (Ni-TMA-MOF/NF). When tested as an electrocatalyst for benzyl alcohol oxidation, Ni-TMA-MOF/NF exhibited lower overpotential and superior durability compared to Ni foam-loaded Ni-based terephthalic MOF electrocatalyst (Ni-PTA-MOF/NF) and Ni(OH)2 nanosheet array (Ni(OH)2/NF). Ni-TMA-MOF/NF required only a low potential of 1.65 V to achieve a high current density of 400 mA cm-2. Even after 40000 s of electrocatalytic oxidation at 1.5 V, Ni-TMA-MOF/NF maintained a current density of 175 mA cm-2 with ∼68% retention, showing its potential for benzyl alcohol oxidation. Through a combination of experimental and theoretical investigations, it was found that Ni-TMA-MOF/NF displayed superior electrocatalytic activity due to an optimized electron structure with high-valence Ni species and a high density of active sites, enabling long-term stable operation at high current densities. This study provides a new perspective on the design of electrocatalysts for benzyl alcohol oxidation.

Spin-Magnetic Effect of d-π Conjugation Polymer Enhanced O-H Cleavage in Water Oxidation.

A deep understanding of the mechanism for the spin-magnetic effect on O-H cleavage is crucial for the development of new catalysts for water oxidation. Herein, we designed and synthesized the crystalline Fe-DABDT and Co-DABDT (DABDT = 2,5-diaminobenzene-1,4-dithiol) and optimized an effective magnetic moment to explore the role of the spin-magnetic effect in the regulation of water oxidation activity. It can be found that the OER activity of the catalyst is positively correlated with its effective magnetic moment. Under the external magnetic field, Fe-DABDT with more spin single electrons has a stronger spin-magnetic response to water oxidation than Fe/Co-DABDT and Co-DABDT. The increase in OER current of Fe-DABDT is nearly 2 times higher than that of Co-DABDT. Experimental and density functional theory studies show that magnetized Fe sites could realize nucleophilic reaction, accelerate the polarization of electron spin states, and promote the polar decomposition of O-H and the formation of the O-O bond. This study provides mechanistic insight into the spin-magnetic effect of oxygen evolution reaction and further understanding of the spin origin of catalytic activity, which is expected to improve the energy efficiency of hydrogen production.

Indole inhibited the expression of csrA gene in Escherichia coli.

Indole is a very important signal molecule which plays multiple regulatory roles in many physiological and biochemical processes of bacteria, but up to now, the reasons for its wide range of functions have not been revealed. In this study, we found that indole inhibits the motility, promotes glycogen accumulation and enhances starvation resistance of Escherichia coli. However, the regulatory effects of indole became insignificant while the global csrA gene was mutated. To reveal the regulatory relationship between indole and csrA, we studied the effects of indole on the transcription level of csrA, flhDC, glgCAP and cstA, and also the sensing of the promoters of the genes on indole. It was found that indole inhibited the transcription of csrA, and only the promoter of the csrA gene can sense indole. Namely, indole indirectly regulated the translation level of FlhDC, GlgCAP and CstA. These data indicates that indole regulation is related with the regulation of CsrA, which may throw light on the regulation mechanism research of indole.

"Polyoxometalate electron sponge" induces the accurate regulation of electron states at Ni sites to enhance oxidation of water.

Because of their special features, NiFe-LDHs (nickel iron layered double hydroxides) are prospective OER (oxygen evolution reaction) catalysts that might be utilized to catalyse the electrolysis of water and produce hydrogen to address the energy crisis. In this work, the electronic structure and electrocatalytic performance of the NiFe-LDH were accurately regulated by optimizing the Ni sites, which was enabled by adjacent metal sites coordinated with the "polyoxometalate electron sponge". With extension of the modification time, the Ni 2p binding energy, the Ni3+/Ni2+ ratio and the OER properties were gradually tuned, which indicated accurate regulation of active Ni sites by the "polyoxometalate electron sponge" on a temporal scale. Additionally, NiFe-LDH-PW12-12 h (NiFe-LDH modified by polyoxometalate anions for 12 h) showed the highest OER performance along with fast electron transfer, superior reaction kinetics and electrochemical durability, with an overpotential ∼68 mV lower than that of NiFe-LDH. This work provides an accurate strategy for regulating the electronic structures of active metal sites for the OER.

Highly Ordered Hierarchical Macro-Mesoporous Carbon-Supported Cobalt Electrocatalyst for Efficient Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) and their derivatives have been extensively employed in Oxygen Evolution Reaction (OER) catalysts due to their significantly larger specific surface areas, distinct metal centers, and well-organized porous structures. However, the microporous structure of MOFs and their derivatives presents mass transfer resistance, limiting their further development. Drawing inspiration from hierarchical structures allowing for the transport and exchange of substances in the biological world, we designed and fabricated biomimetic layered porous structures within ZIF-67 and its derivatives. Based on this, we achieved a three-dimensional ordered layered porous nitrogen-doped carbon-coated magnetic cobalt catalyst (3DOLP Co@NDC) with a biomimetic pore structure. It is found that the 3DOLP Co@NDC (352 mV @10 mA cm-1) was better than Co@NDC (391 mV @10 mA cm-1). The introduction of a three-dimensional ordered layered porous structure is conducive to increasing the specific surface area of the material, increasing the electrochemical active area, and improving the catalytic performance of the material. The introduction of a three-dimensional ordered layered porous structure would help to build a bionic grade pore structure. The existence of biomimetic grade pore structure can effectively reduce the mass transfer resistance, improve the material exchange efficiency, and accelerate the reaction kinetics.

Single-Atom Mn Catalysts via Integration with Mn Sub Nano-Clusters Synergistically Enhance Oxygen Reduction Reaction.

Integrating single atoms and clusters into one system represents a novel strategy for achieving the desired catalytic performance. In comparison to single-atom catalysts, catalysts combining single atoms and clusters harness the advantages of both, thus displaying greater potential. Nevertheless, constructing single-atom-cluster systems remains challenging, and the fundamental mechanism for enhancing catalytic activity remains elusive. In this study, a directly confined preparation of a 3D hollow sea urchin-like carbon structure (MnSA/MnAC-SSCNR) is developed. Mn single atoms synergistically interact with Mn clusters, optimizing and reducing energy barriers in the reaction pathway, thus enhancing reaction kinetics. Consequently, in contrast to Mn single-atom catalysts (MnSA-SSCNR), MnSA/MnAC-SSCNR exhibits significantly improved oxygen reduction activity, with a half-wave potential (E1/2) of 0.90 V in 0.1 m KOH, surpassing that of MnSA-SSCNR and Pt/C. This work demonstrates a strategy of remote synergy between heterogeneous single atoms and clusters, which not only contributes to electrocatalytic reactions but also holds potential for reactions involving more complex products.

The complete mitochondrial genome of Syrista parreyssii (Spinola, 1843) (Hymenoptera: Cephidae) and its phylogenetic analyses.

The complete mitochondrial genome of Syrista parreyssii (Spinola, 1843) was described. The circular genome is 18,666 bp with an A + T content of 82.60%. It contains 37 genes and a 1921 bp control region. The CR-trnI (+)-trnQ (-)-trnM (+) cluster is rearranged as trnM (+)-CR-trnQ (-)-trnI (+) cluster. Phylogenetic analysis demonstrates that European Syrista and Asian Neosyrista were not sister groups. Neosyrista is a valid genus and should be reestablished. Moreover, a preliminary study based on COI showed there are at least three valid Syrista species within the European and Mediterranean regions. Whether the known Syrista parreyssii (Spinola, 1843) is a complex or there are more cryptic species needs further study.

Hierarchical hollow zeolite fiber in catalytic applications: A critical review.

Zeolites have widely been studied because of the better performance as catalysts and supports. However, the zeolites with only micropores have drawbacks in reactivity and selectivity due to limitation of diffusivity. The hollow zeolite fibers (HZF) with hierarchical porosity however can overcome the problem. The HZF can be synthesized by such methods as incorporated substrate removal method, solid-solid transformation method, co-axial electrospinning technology, dry-wet spinning technology, and hollow fiber incorporation method. The unique hierarchical porous structure leads to the great improvement in the diffusion efficiency of reactants. The catalytic zeolite membrane fibers are the most commonly used as they have stronger catalyst stability and higher catalytic selectivity. The HZFs are suitable in catalytic applications such as selective catalysis, CO preferential oxidation, air purification and wastewater treatment. In order that the HZFs can be applied to industrial operations, more research work should be carried out, such as developments of self-assembly pure HZFs, catalytic substrate incorporated HZFs, HZFs with gradient multicomponent zeolites and HZFs with nanoscale diameters.

Regulating the Spin State of FeIII Enhances the Magnetic Effect of the Molecular Catalysis Mechanism.

Aqueous-phase oxygen evolution reaction (OER) is the bottleneck of water splitting. The formation of the O-O bond involves the generation of paramagnetic oxygen molecules from the diamagnetic hydroxides. The spin configurations might play an important role in aqueous-phase molecular electrocatalysis. However, spintronic electrocatalysis is almost an uncultivated land for the exploration of the oxygen molecular catalysis process. Herein, we present a novel magnetic FeIII site spin-splitting strategy, wherein the electronic structure and spin states of the FeIII sites are effectively induced and optimized by the Jahn-Teller effect of Cu2+. The theoretical calculations and operando attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR) reveal the facilitation for the O-O bond formation, which accelerates the production of O2 from OH- and improves the OER activity. The Cu1-Ni6Fe2-LDH catalyst exhibits a low overpotential of 210 mV at 10 mA cm-2 and a low Tafel slope (33.7 mV dec-1), better than those of the initial Cu0-Ni6Fe2-LDHs (278 mV, 101.6 mV dec-1). With the Cu2+ regulation, we have realized the transformation of NiFe-LDHs from ferrimagnets to ferromagnets and showcase that the OER performance of Cu-NiFe-LDHs significantly increases compared with that of NiFe-LDHs under the effect of a magnetic field for the first time. The magnetic-field-assisted Cu1-Ni6Fe2-LDHs provide an ultralow overpotential of 180 mV at 10 mA cm-2, which is currently one of the best OER performances. The combination of the magnetic field and spin configuration provides new principles for the development of high-performance catalysts and understandings of the catalytic mechanism from the spintronic level.

Tuning the oxygen vacancy of mixed multiple oxidation states nanowires for improving Li-air battery performance.

Mixed multiple oxidation states CoMoO4 nanowires (electrocatalysts) with tunable intrinsic oxygen vacancies were fabricated. CoMoO4 with proper oxygen vacancy can be employed to construct a Li-air battery with a high capacity and stable cyclability. This is possible because CoMoO4 contains surface oxygen vacancies, which result in the unit of CoMo bond, that is important for electrocatalysts used in Li-air batteries. Both the experimental and theoretical results demonstrate that the surface oxygen vacancies containing CoMoO4 nanowires have a higher electrocatalytic activity. This shows that the highly efficient electrocatalysts used for Li-air batteries were designed to modify the redox properties of the mixed metal oxide in the catalytic active sites. This successful material design led to an improved strategy for high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities based on the fast formation and extinction of ORR products.

The complete mitochondrial genome of Taxoblenus sinicus Wei & Nie, 1999 (Hymenoptera: Tenthredinidae) and phylogenetic analysis.

The complete mitochondrial genome of Taxoblenus sinicus Wei & Nie, 1999 was described. The circular genome is 15,878 bp with an A + T content of 80.4%. It contains 37 genes, and an 859 bp control region. The trnI (+)-trnQ (-)-trnM (+) cluster rearranges to trnM (+)-trnQ (-)-CR-trnI (+). Phylogenetic analysis demonstrates that Allantinae is a sister group of Tenthredininae and T. sinicus is one of the basal lineages of Allantinae.

The complete mitochondrial genome of Allantus togatus (Panzer, 1801), in view of possible cryptic species.

The complete Allantus togatus (Panzer, 1801) mitogenome was determined and analyzed. The mitogenome contains typical 37 genes with identical order to Allantoides luctifer mitogenomes. Phylogenetic analysis revealed that A. togatus clustered together with A. viennensis. The wide genetic distances found between lineages of A. togatus lead to the assumption of cryptic species. These complete mitogenomes provide valuable information at the genomic level that can be utilized to sustain bioresources to deepen the understanding of cryptic diversity within Allantinae.

[Synthetic biology for the synthesis of mogroside V - a review].

Mogroside V, a component with high content and sweetness in mogrosides, has many pharmacological activities such as relieving cough, reducing sputum, anti-cancer, anti-oxidation, regulating blood sugar, making it a natural nonsugar sweetener with therapeutic functions, and showing a broad market prospect. However, the limited resources and high extraction costs have restricted its widespread use. The rapid development of synthetic biology has provided a new idea for the production of plant natural products. The low-cost and large-scale production will be realized through the construction of a microbial cell factory for mogroside V. Here, we briefly introduce the structure and pharmacological activity of mogroside V, and review progress in applying synthetic biology for its synthesis, and also discuss the challenges faced by the current research, to provide a reference for further studies on the biosynthesis of mogroside V.

"Lewis Base-Hungry" Amorphous-Crystalline Nickel Borate-Nickel Sulfide Heterostructures by In Situ Structural Engineering as Effective Bifunctional Electrocatalysts toward Overall Water Splitting.

The development of high-performance, low-cost, and long-lasting electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is urgently needed for effective electrochemical water splitting. In the present study, an engineering process was employed to prepare "Lewis base-hungry" amorphous-crystalline nickel borate-nickel sulfide (Ni3(BO3)2-Ni3S2) heterostructures, which exhibited unprecedentedly high electrocatalytic activity toward both OER and HER in alkaline media. The optimal Ni3(BO3)2-Ni3S2/nickel foam (Ni3(BO3)2-Ni3S2/NF) electrode displayed an ultralow overpotential of only -92 and +217 mV to reach the current density of 10 mA cm-2 for HER and OER, respectively. When the Ni3(BO3)2-Ni3S2/NF electrode was used as both the anode and cathode for overall water splitting, a low cell voltage of 1.49 V was needed to achieve the current density of 10 mA cm-2, which was superior to the performance of most noble metal-free electrocatalysts. Results from density functional theory calculations showed that the Lewis base-hungry sites in the heterostructures effectively enhanced the chemisorption of hydrogen and oxygen intermediates, a critical step in HER and OER electrocatalysis. Results from this study highlight the significance of rational design and engineering of heterostructured materials for the development of high-efficiency electrocatalysts.

Engineering Lithium Ions Embedded in NiFe Layered Double Hydroxide Lattices To Activate Laminated Ni2+ Sites as High-Efficiency Oxygen Evolution Reaction Catalysts.

NiFe layered double hydroxides (LDHs) have been denoted as benchmark non-noble-metal electrocatalysts for the oxygen evolution reaction (OER). However, for laminates of NiFe LDHs, the edge sites are active, but the basal plane is inert, leading to underutilization as catalysts for the OER. Herein, for the first time, light and electron-deficient Li ions are intercalated into the basal plane of NiFe LDHs. The results of theoretical calculations and experiments both showed that electrons would be transferred from near Ni2+ to the surroundings of Li+ , resulting in electron-deficient properties of the Ni sites, which would function as "electron-hungry" sites, to enhance surface adsorption of electron-rich oxygen-containing groups, which would enhance the effective activity for the OER. As demonstrated by the catalytic performance, the Li-NiFe LDH electrodes showed an ultralow overpotential of only 298 mV at 50 mA cm-2 , which was lower than that of 347 mV for initial NiFe LDHs and lower than that of 373 mV for RuO2 . Reasonable intercalation adjustment effectively activates laminated Ni2+ sites and constructs the electron-deficient structure to enhance its electrocatalytic activity, which sheds light on the functional treatment of catalytic materials.

Morphology-Controlled Synthesis of Ni-MOFs with Highly Enhanced Electrocatalytic Performance for Urea Oxidation.

MOFs present potential application in electrocatalysis. The structure-activity of the Ni-MOFs with different morphologies, nanowires, neurons, and urchins is systemically investigated. The Ni-MOFs were controllably synthesized via the facile solvothermal method. Among them, the Ni-MOF nanowires are endowed with the highest electrocatalytic activity due to the unique structure, more exposed active sites, lower charge transfer resistance, and the fast and direct electron transfer in 1D structures. The typical morphology of the Ni-MOF nanowires is ca. 10 nm in diameter and several micrometers in length. When employed as an electrocatalyst in urea oxidation reaction, it exhibits a lower overpotential than and superior stability to the Ni-MOFs with other morphologies. Ni-MOF nanowires require a potential of ∼0.80 V (vs Ag/AgCl) to obtain 160 mA cm-2. In addition, after continuous electrocatalyzing for 3600 s at 0.40 V (vs Ag/AgCl), the current density retention of Ni-MOF nanowires could still reach more than 60% (>12 mA cm-2), which demonstrates Ni-MOF nanowires as promising electrocatalysts for urea oxidation.

Needle grass-like cobalt hydrogen phosphate on Ni foam as an effective and stable electrocatalyst for the oxygen evolution reaction.

Exploring efficient non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is a challenging task in sustainable energy systems. Herein, facile and novel three dimensional (3D) needle grass-like CoHPO4·H2O on Ni foam (CoHPO/NF) has been prepared as an effective and robust OER electrocatalyst for the first time. The unique 3D topological structure of CoHPO exposes more electrocatalytic active sites and facilitates mass transport. The coordinated HPO42- anions work as OH- traps to synergistically enhance the process of the OER. Because of these advantages, it exhibits an extraordinary OER performance with a low overpotential of only 350 mV at 50 mA cm-2. Notably, it also exhibits excellent long-term stability. According to the theoretical calculations, the electron structure of the Co was significantly influenced by the coupled HPO42- species, which leads to superior activity for the OER. All the findings imply that CoHPO/NF is a promising material to substitute for noble metals in overall water splitting.

3D Porous Amorphous γ-CrOOH on Ni Foam as Bifunctional Electrocatalyst for Overall Water Splitting.

The development of novel and highly efficient bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an ongoing challenge. The Cr3+ cation has a special electronic configuration (t32ge0g), which facilitates charge transfer and electron capture. However, Cr-based materials applied on water-splitting electrocatalysis is still a research void up to now. Herein, a novel amorphous γ-CrOOH was developed as a bifunctional electrocatalyst toward overall water splitting for the first time. It shows extraordinary HER activity with an ultralow overpotential of only 149 mV at 50 mA cm-2. Meantime, there is a small overpotential of 334 mV at 50 mA cm-2 for the OER. Importantly, the bifunctional electrocatalyst for overall water-splitting electrocatalysis can work with a cell voltage of merely 1.56 V at 10 mA cm-2. Amorphous γ-CrOOH has effectively enhanced the intrinsic electrochemical activity via density functional theoretical calculations. Therefore, this work not only provides a new method for preparation of amorphous γ-CrOOH but also expands the types of catalysts for water splitting.

Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets with the Inherent Open Active Sites as Electrocatalysts in Aprotic Li-O2 Batteries.

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have the potential to improve the performance of Li-O2 batteries with high O2 accessibility, open catalytic active sites, and large surface areas. To obtain highly efficient cathode catalysts for aprotic Li-O2 batteries, a facile ultrasonicated method has been developed to synthesize three kinds of 2D MOFs (2D Co-MOF, Ni-MOF, and Mn-MOF). Contributing from the inherent open active sites of the Mn-O framework, the discharge specific capacity of 9464 mAh g-1 is achieved with the 2D Mn-MOF cathode, higher than those of the 2D Co-MOF and Ni-MOF cathodes. During the cycling test, the 2D Mn-MOF cathode stably operates more than 200 cycles at 100 mA g-1 with a curtailed discharge capacity of 1000 mAh g-1, quite longer than those of others. According to further electrochemical analysis, we observe that the 2D Mn-MOF outperforms 2D Ni-MOF and Co-MOF due to a superior oxygen reduction reactions and oxygen evolution reactions activity, in particular, the efficient oxidation of both LiOH and Li2O2. The present study provides new insights that the 2D MOF nanosheets can be well applied as the Li-O2 cells with high energy density and long cycling life.